Denver has a consolidated city and county government with both a sheriff's department and a police department. The sheriff's department runs the jail and is the law enforcement arm of the courts that provides security at the court houses, conducts evictions, seizes property to pay for judgments and serves process. The police department, in contrast, is the crime fighting and traffic control force of the city and county.
The sheriff's deputy has limited arrest powers in connection with crimes committed in jail, but doesn't have the full power to make arrests that police do. So, a sheriff's deputy on the way home from work, for example, has no more power to arrest people than any other ordinary citizen. They want that power, and the city has refused to grant it to them.
The city doesn't want to pay for the training that law enforcement officers with full arrest powers must receive, doesn't want to pay the wages that more highly trained jail guards would command, and, doesn't want to have hundreds of law enforcement officers outside the usual chain of command in the police department roaming the streets and creating a risk of liability to them. The city has a hard enough time preventing its regular police officers from engaging in liability creating misconduct.
The union for the sheriff's deputies (the Fraternal Order of Police) tried to do an end run around the decision made by Mayor Hickenlooper's administration and the City Council with a ballot initiative. They needed 41,666 signatures to get on the ballot in a special election in February (which would have cost the city $750,000-$1,000,000). They turned in a little less than 57,395 signatures by the deadline.
I heard rumors that the signature collect quality was very low. For example, ballot officials found apparently forged signatures of people who were actively campaigning against the measure. It isn't that the sheriff's deputies were dishonest, they just "hired a company to collect the signatures" which didn't have high enough standards. This is a long standing problem when your workforce is made up of temporary unskilled workers who are rewarded, directly or indirectly, for producing more signatures. The validity percentage in this case was spectularly low, however.
According to Stephanie O'Malley, the City and County's new elected Clerk and Recorder, the union turned in 22,229 valid signatures and 34,166 invalid signatures. Unless they can cure 19,437 signatures by November 12, the initiative won't go on the ballot, although O'Malley's decision is subject to deferrential court review. Realistically, I'd be stunned if the union could cure that many signatures in time.
Arrest Powers As Gun Control
The debate is, to some extent, a derviative of the gun control debate. The Second Amendment constitution right to be armed for self-defense, subject to reasonable restricts, was established in the Heller case decided by the U.S. Supreme Court by a police officer who wasn't allowed to have a handgun in his own District of Columbia home for personal self-defense. The explicit recognition in Heller of a crime prevention element of the Second Amendment refocuses the debate on who may do what to prevent crimes.
There are two distinctions between the arrest powers of private citizens and law enforcement officers. The first is that private citizens can only arrest people for crimes committed in their presence, and the second is that law enforcement offices, but not private citizens, may use deadly force arrest high risk suspects. Thus, law enforcement officers have greater authority to use guns to arrest people for crimes than private citizens do.
A private citizen in Colorado is permitted to use "appropriate physical force" which "he he reasonably believes is necessary" to arrest someone who "has committed an offense in his presence." Private citizens aren't permitted to use deadly force strictly for the purpose of making an arrest on their own account, or to arrest someone for a crime that someone else says they saw committed.
As a general rule, enforcement of the law through armed vigilantees isn't permitted. Someone using a gun to make an arrest can be criminally prosecuted and sued for doing so, even if the person arrested really was a criminal and a police officer could have legally arrested that person.
Of course, often, in isolated incidents where the arrest would otherwise have been lawful, the District Attorney's office and police will exercise their discretion to take no action against the private citizen, and someone who is later prosecuted and convicted of a crime will have a hard time making a case that the illegal private arrest caused anything more than nominal damages.
Private citizens have no power to used deadly force to make an arrest, separate from the general privilege of all people to use deadly force to protect yourself and others. Even felons prohibited from owning guns have this narrow privilege, although the tools they are allowed to use in doing so is limited to cruder weapons like cars and kitchen knives and clubs, rather than firearms.
The only real except to this rule is that private citizens can also use any kind of force to make an arrest of anyone under the direction of a law enforcement officer, so long as that citizen doesn't personally know to be an illegal direction.
In contrast, a law enforcement officer need only have a "reasonable belief that a person has committed an offense" (a warrant or probable cause are two means of obtaining that belief) to arrest that person. A law enforcement officer may use deadly force in carrying out that arrest if officer believes tha the person used or attempted to use a deadly weapon in a felony or attempted felony, or is likely to endanger human life or inflict serious injury on another if not apprehended without delay (mere traffic violations don't suffice to establish this risk).
Arrests in Colorado are spelled out at Colorado Revised Statutes Sections 16-3-101 to 16-3-203, and Section 18-1-707.)
Since sheriff's deputies already have arrest powers when they are engaged in guarding jails, the primary effect of the intiative they proposed would be to turn off duty sheriff's officers into an unorganized militia or citizen's watch, at least when on duty (e.g. out serving process or en route to an eviction), or employed as a private security guard with city permission.